The Constructor

Water-reducing Set-retarding Admixtures: Affects, and Applications

Water-reducing Set-retarding Concrete Admixture

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Water-reducing and set-retarding admixtures are chemicals that slow down the initial reaction between cement and water by reducing the rate of water penetration to the cement and slowing down the growth of the hydration products.

As a result, concrete stays workable longer than it would otherwise. The length of time during which a concrete remains workable depends on its temperature, consistence class, and water-cement ratio, and on the amount of retarder used.

Retarded concrete needs careful proportioning to minimize bleeding due to the longer period during which the concrete remains fresh. It permits placement of large volumes of concrete over extended periods, minimizing the need for forming, placing, and joining separate units.

Effects on Fresh Concrete

Fig. 1: Reduce Water Content in Concrete Using Admixtures

Effects on Hardened Concrete


According to ACI 212.3R, the dosage of the admixture should be determined from information provided by one or more of the following sources:

  1. Results from construction works where the admixture employed under good field control, preferably using the same materials and under conditions similar to those expected.
  2. Laboratory tests carried out to evaluate the admixture.
  3. Information and technical literature from the manufacturer.
Fig. 2: Dosage


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